1. Field of the Invention
The present invention relates to a pulverized fuel combustion burner to be applied to a boiler of a thermal power plant or chemical plant, a furnace of a chemical plant or the like.
2. Related Art
A technique of the prior art will be described with reference to FIGS. 5(a)-(c). FIGS. 5(a) to 5(c) are side sections showing a construction of a pulverized fuel combustion burner schematically. FIGS. 5(a), 5(b) and 5(c) show the cases, respectively, in which a mixed flow of a pulverized fuel and carrier air is injected horizontally, in which the mixed flow is injected upwardly, and in which the mixed flow is injected downwardly.
Reference numeral 1 designates a primary air nozzle, (also more simply referred to as the xe2x80x98primary nozzlexe2x80x99) and numeral 2 designates a secondary air nozzle (also more simply referred to as the xe2x80x98secondary nozzlexe2x80x99) arranged outside of the primary air nozzle 1. Numeral 3 designates a pulverized fuel supply pipe, and numeral 4 designates a combustion auxiliary fuel supply passage which is defined by the pulverized fuel supply pipe 3 and a windbox 5. The pulverized fuel supply pipe 3 communicates with the primary air nozzle 1, and its terminal end, and the combustion auxiliary air supply passage 4 communicates with the secondary air nozzle 2.
Reference numeral 10 designates a rich/lean flow separator which is arranged in the pulverized fuel supply pipe 3 so that a mixed flow 7 of the pulverized fuel and the carrier air, flowing through the pulverized fuel supply pipe 3, may impinge upon the rich/lean flow separator 10 and may be separated by the action of centrifugal force into a relatively rich flow 8 (as indicated by solid lines) to flow along the outer side and a lean flow 9 (as indicated by broken lines) to flow along the inner side.
Here, reference numeral 12 designates a clearance which is established between the furnace side end portion of the windbox 5 and the windbox side end portion of the secondary air nozzle 2 when the secondary air nozzle 2 is directed upward, as shown in FIG. 5(b), or downward, as shown in FIG. 5(c), by xcex8 degrees.
Under ordinary operation, the mixed flow 7 of the pulverized fuel and the carrier air is guided through the pulverized fuel supply pipe 3 into the primary air nozzle 1 so that it is injected into the furnace. On the other hand, the combustion auxiliary air is guided through the combustion auxiliary air supply passage 4 into the secondary air nozzle 2 so that it is injected into the furnace.
In order to satisfy performances criteria for a low Nox combustion required from a combustion aspect, both the relatively rich and lean flows 8 and 9 of the pulverized fuel, as separated after the mixed flow 7 is separated by the action of the rich/lean flow separator 10, have to maintain a proper concentration distribution on a furnace side exit plane of the primary air nozzle 1.
Moreover, the combustion auxiliary air has to be injected as wholly as possible through the secondary air nozzle 2 into the furnace to thereby make an effective contribution to the combustion.
FIG. 5(a) shows the state in which the mixed flow 7 and the combustion auxiliary air are injected horizontally into the furnace. In this burner of the prior art, the injection direction of the mixed flow 7 and the combustion auxiliary air into the furnace can be changed upward or downward by directing the primary air nozzle 1 and the secondary air nozzle 2 upward or downward, respectively, as shown in FIGS. 5(b) and 5(c). As a result, the position of the flame to be maintained in the furnace can be moved upward or downward in the furnace to thereby adjust the gas temperature distribution in the furnace and the gas temperature at the furnace exit plane.
In the burner of the prior art thus far described, the mixed flow 7 of the pulverized fuel and carrier air can achieve the proper concentration distribution in the furnace side exit plane of the primary air nozzle 1 when it is injected horizontally into the furnace, as shown in FIG. 5(a). When the primary air nozzle 1 is directed upward or downward, respectively, as shown in FIG. 5(b) or 5(c), on the other hand, the relatively rich flow 8 of the pulverized fuel is biased, causing a problem in that the mixed flow 7 cannot establish the proper rich/lean distribution in the furnace side exit plane of the primary air nozzle 1 like the state shown in FIG. 5(a).
Moreover, the combustion auxiliary air has to pass as wholly as possible through the secondary air nozzle 2. When the secondary air nozzle 2 is directed upward or downward, however, the clearance 12 is established, as shown in FIGS. 5(b) and 5(c), between the furnace side end portion of the windbox 5 and the windbox side end portion of the secondary air nozzle 2. As a result, a portion of the combustion auxiliary air bypasses the secondary air nozzle 2 from that clearance 12 and leaks into the furnace, causing a problem in that the combustion auxiliary air does not make an effective contribution to combustion.
The invention contemplates resolving the problems of the prior art and has an object of providing a pulverized fuel combustion burner which can maintain the concentration distribution of the pulverized fuel and can eliminate the leakage of the combustion auxiliary air.
In order to achieve the above-specified object, according to an aspect of the invention, there is provided a pulverized fuel combustion burner comprising a plurality of air nozzles arranged on a side wall of a furnace for injecting a mixed flow of a pulverized fuel and carrier air to establish a flame. The burner includes a primary air nozzle having a variable direction to inject the mixed flow into the furnace, a secondary air nozzle for feeding combustion auxiliary air around the primary air nozzle, a pulverized fuel supply for feeding the mixed flow to the primary air nozzle and a windbox having the pulverized fuel supply pipe extend therethrough for forming a combustion auxiliary air supply passage around the pulverized fuel supply pipe. The windbox is constructed by arranging unit windboxes in a separate or jointed relation with each other. Each unit windbox has at least one pulverized fuel supply pipe and one combustion auxiliary air supply passage. A rich/lean flow separator is disposed at or near a jointed portion between the primary air nozzle and the pulverized fuel supply pipe. The rich/lean flow separator is able to change its direction in response to or independently of a change in an injection direction of the primary air nozzle.
Specifically, the rich/lean flow separator is arranged at or near the jointed portion between the primary air nozzle and the pulverized fuel supply pipe, and the rich/lean flow separator is able to change its direction in response to or independently of the change in the injection direction of the primary air nozzle. Thus, when the primary air nozzle changes its injection direction upward or downward, for example, the rich/lean flow separator follows the direction change so that the mixed air of the rich and lean flows separated thereby is injected without any bias and in accordance with the direction of the primary air nozzle.
According to another aspect of the invention, there is provided a pulverized fuel combustion burner further comprising another rich/lean air separator disposed upstream of the first rich/lean flow separator. Specifically, upstream of the rich/lean flow separator disposed at or near the jointed portion between the primary air nozzle and the pulverized fuel supply pipe, there is disposed another rich/lean flow separator. Thus, the rich/lean flow separation is made at first by the rich/lean flow separator positioned upstream, and then is further made by taking over the separation effect at or near the jointed portion which is near the injection port between the primary air nozzle and the pulverized fuel supply pipe, while still following direction changes in accordance with upward or downward movement of the primary air nozzle.
According to a further aspect of the invention, there is provided a pulverized fuel combustion burner comprising a plurality of air nozzles arranged on a side wall of a furnace for injecting a mixed flow of a pulverized fuel and carrier air to establish a flame. The air nozzles include a primary air nozzle having a variable direction to inject the mixed flow into the furnace, a secondary air nozzle for feeding combustion auxiliary air to around the primary air nozzle, a pulverized fuel supply pipe for feeding the mixed flow to the primary air nozzle and a windbox receiving the pulverized fuel supply pipe therethrough for forming a combustion auxiliary air supply passage around the pulverized fuel supply pipe. The windbox is being constructed by arranging unit windboxes in a separated or jointed relation with respect to each other. Each unit windbox has at least one pulverized fuel supply pipe and one combustion auxiliary air supply passage. A rich/lean flow separator is disposed in the pulverized fuel supply pipe and a flow straightener or a straightening plate is disposed in at least one of the primary air nozzle and the pulverized fuel supply pipe for maintaining a concentration distribution, as established by the rich/lean flow separator up to an exit of the primary air nozzle.
That is, subsequent to the rich/lean flow separator disposed in the pulverized fuel supply pipe, more specifically, a flow straightener or a straightening plate is disposed in at least one of the primary air nozzle and the pulverized fuel supply pipe. As a result, the effect of the rich/lean flow separator is taken over by the flow straightener or the straightening plate so that the rich flow and the lean flow are carried in a separated state and injected through the primary air nozzle into the furnace.
According to a further aspect of the invention, there is provided a pulverized fuel combustion burner further comprising a combustion auxiliary air flow straightener disposed in the windbox for guiding the combustion auxiliary air into an entrance of the secondary air nozzle. Specifically, the leakage of combustion auxiliary air at the entrance of the secondary air nozzle can be drastically prevented not only by devising the primary air nozzle for guiding the mixed flow of the pulverized fuel and the carrier air preferably but also by guiding the combustion auxiliary air to the entrance of the secondary air nozzle with the combustion auxiliary air flow straightener disposed in the windbox.
According to a further aspect of the invention, there is provided a pulverized fuel combustion burner wherein the primary air nozzle is disposed at a corner portion of the side wall of the furnace. Specifically, the burner is devised to separate the mixed flow of the pulverized fuel and the carrier air into the rich flow and the lean flow with the pulverized fuel supply pipe and the primary air nozzle and to maintain the separation effect. The burner is arranged at the corner portion of the furnace side wall so that a preferable injection may be effected from the corner portion into the furnace.
According to a further aspect of the invention, there is provided a pulverized fuel combustion burner wherein the windbox comprises a plurality of unit windboxes, each having a square front section and each having at least one pulverized fuel supply pipe and one combustion auxiliary air supply passage. The unit windboxes are arranged in a separated or jointed relation with respect to each other, and the unit windbox has an upward and downward directional length of one and a half (1.5) times or less of its lateral directional length.
Specifically, the unit windbox is constructed by housing the primary air nozzle, which is devised to separate the mixed flow of the pulverized fuel and the carrier air with the pulverized fuel supply pipe and the primary air nozzle and to keep the separation effect, and the secondary air nozzle which prevents the leakage of the combustion auxiliary air at its entrance. The unit windbox has an upward and downward directional length of one and a half (1.5) times or less its lateral directional length, thereby making the entire construction compact without lowering the performance.